Conventionally, as a linear guide device constituting a linear guide portion of a machine tool, industrial robots of various types, or the like, there has been known one including a linear or an arcuate track rail having a longitudinally extending ball rolling surface and a slider assembled to the track rail through the intermediation of a large number of balls. The slider is equipped with a load rolling surface opposed to the ball rolling surface of the track rail, and a circulation path for endless circulation of the large number of balls rolling between the load rolling surface and the track rail rolling surface while bearing load. By causing the balls to circulate through the endless circulation path, the slider can continuously move over the entire length of the track rail.
Usually, the track rail is fixed to a base portion such as a bed or a column of a machine tool or the like through fastening by fixation bolts. Thus, the track rail has, at predetermined longitudinal intervals, bolt installation holes through which the fixation bolts are to be passed. If the head portions of the fixation bolts protrude beyond the track rail, they constitute an obstacle when the slider moves along the track rail, so the interior of each bolt installation hole includes a small diameter portion and a large diameter portion. The small diameter portion has an inner diameter slightly larger than the nominal diameter of the bolt, and the large diameter portion has an inner diameter slightly larger than the diameter of the bolt head portion. That is, the large diameter portion constitutes an accommodating portion for the bolt head portion, preventing the bolt head portion from protruding beyond the surface of the track rail.
It should be noted, however, that such bolt installation holes allow foreign matter such as work chips or coolant liquid of the machine tool to enter the slider moving along the track rail. Within the slider, the balls are circulating, bearing load between the slider and the track rail; if foreign matter such as work chips or dust enters the slider, flaws will be generated in the rolling surface of the track rail, the load rolling surface of the slider, and the balls, or wear of those components will be promoted, resulting in premature impairment of the movement precision of the slider of the linear guide device. Further, if coolant liquid, which is used in the machine tool to cool work, is allowed to enter the slider, the lubricant oil adhering to the ball surfaces will be washed away, resulting in premature wear of the rolling surface and the balls. In order to prevent foreign matter from entering the slider, a seal member in sliding contact with the surface of the track rail is provided around the slider, removing foreign matter adhering to the surface of the track rail as the slider moves. However, when bolt installation holes are provided in the track rail, foreign matter is allowed to enter the slider through the bolt installation holes, so the effect of the seal member is diminished. Further, the seal member is held in contact with the surface of the track rail with a certain degree of fastening force, so, when the bolt installation holes exist, the forward end portion of the seal member is rubbed against the opening edges of the bolt installation holes, resulting in premature deterioration of the seal member.
In view of this, when the linear guide device is used in an environment where foreign matter is likely to adhere to the track rail, closing caps are fitted to the bolt installation holes of the track rail after the mounting of the track rail to the base portion by fixation bolts, thus closing the bolt installation holes. The closing caps are fit-engaged with the large diameter portions of the bolt installation holes while covering the head portions of the fixation bolts accommodated in the large diameter portions, with the closing caps being flush with the surface of the track rail.
JP 05-138428 A and JP 2002-48138 A disclose metal closing caps as examples of the closing caps. Those metal closing caps have an outer diameter that is the same as or slightly larger than the inner diameter of the large diameter portions of the bolt installation holes. By being forced into the bolt installation holes, those metal closing caps are firmly fixed to the openings of the bolt installation holes. More specifically, the following forcing-in method is adopted: after lightly putting the forward end of each closing cap into the bolt installation hole, a flat plate-like jig is applied to the closing cap, and the jig is repeatedly struck by using a tool like a hammer to completely embed the closing cap in the bolt installation hole.
Further, in order to enable each closing cap to be easily forced into the bolt installation hole, and to prevent deformation of the track rail by this forcing-in operation, the closing caps are formed of a metal material whose hardness is lower than that of the metal material forming the track rail. For example, closing caps of copper alloy, aluminum alloy or the like are used for a steel track rail.
Patent Document 1: JP 05-138428 A
Patent Document 2: JP 2002-48138 A